Display device

ABSTRACT

A display device includes pixel electrodes formed in an image display area of a substrate, a common electrode formed in the image display area, inside signal lines formed inside the image display area, and electrically connected to the pixel electrodes, outside signal lines formed outside the image display area, and electrically connected to the inside signal lines, and a common line formed inside and outside the image display area, and electrically connected to the common electrode. An image is displayed under a control of a light using an electric field developed between the pixel electrodes and the common electrode. A coupling capacitance is formed between the inside signal lines and the common electrode. The outside signal lines each include a first portion, and a second portion higher in electric resistance than the first portion and the inside signal lines.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.14/526,807, filed on Oct. 29, 2014, which, is a continuation of U.S.patent application Ser. No.13/851,130(now U.S. Pat. No. 8,878,815),filed on Mar. 27, 2013, which claims the priority from Japanese PatentApplication No. 2012-097266 filed on Apr. 23, 2012 in the JapanesePatent Office, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device.

2. Description of the Related Art

A display device having a touch panel as an interface has been known (JP2008-83491 A). Among a variety of the touch panels, a capacitance touchpanel has been extensively used for a smart phone or the like since thepanel operates smoothly only by touching it with a fingertip. Thedisplay panel is configured such that a display panel laps over thetouch panel.

The display panel is formed with a large number of signal lines thatsupplies image signals for forming an image, and an electromagnetic wavenoise is developed by the image signals. Because the capacitance touchpanel needs to detect a slight change in the capacitance, thesurrounding noise adversely affects a position detection precision.

As a result of the analysis by the present inventors, it is found that acoupling capacitance is formed between a common electrode set to areference potential and the signal lines, and a potential of the commonelectrode is varied according to the image signals that pass through thesignal lines. An electromagnetic wave noise is also generated in thecommon electrode due to the variation in the potential in addition tothe electromagnetic wave noise from the signal lines, resulting in apossibility that the capacitance touch panel malfunctions.

SUMMARY OF THE INVENTION

The invention aims at suppressing a potential variation of a commonelectrode which is set to a reference potential.

(1) According to the invention, there is provided a display deviceincluding: a substrate which has an image display area; pixel electrodeswhich are formed in the image display area of the substrate; a commonelectrode which is formed in the image display area of the substrate;inside signal lines which are formed inside the image display area ofthe substrate, and electrically connected to the pixel electrodes;outside signal lines which are formed outside the image display area ofthe substrate, and electrically connected to the inside signal lines; acommon line which is formed inside and outside the image display area ofthe substrate, and electrically connected to the common electrode, inwhich an image is displayed under a control of a light using an electricfield developed between the pixel electrodes and the common electrode,in which a coupling capacitance is formed between the inside signallines and the common electrode, and in which at least one of the outsidesignal lines and the inside signal lines includes a first portion, and asecond portion that is higher in electric resistance than the firstportion. According to the invention, a signal that is transmitted to theinside signal lines is delayed by the height of electric resistance ofthe second portion when passing through the outside signal lines. A peaklevel of the potential variation of the common electrode which isaffected by the coupling capacitance with the inside signal lines isdecreased. As a result, the potential variation of the common electrodethat is set to the reference potential can be suppressed.

(2) According to the invention, there is provided a display deviceincluding: a substrate which has an image display area; pixel electrodeswhich are formed in the image display area of the substrate; a commonelectrode which is formed in the image display area of the substrate;inside signal lines which are formed inside the image display area ofthe substrate, and electrically connected to the pixel electrodes;outside signal lines which are formed outside the image display area ofthe substrate; switching elements each of which switches electriccontinuity and discontinuity between the inside signal lines and theoutput signal lines; control lines which input a control signal to theswitching elements; and a common line which is formed inside and outsidethe image display area of the substrate, and electrically connected tothe common electrode, in which an image is displayed under a control ofa light using an electric field developed between the pixel electrodesand the common electrode, in which a coupling capacitance is formedbetween the inside signal lines and the common electrode, and in whichthe control lines each include a first portion, and a second portionhigher in electric resistance than the first portion. According to theinvention, the control signal input to the switching element is delayedby the height of electric resistance of the second portion when passingthrough the control lines. Since the operation of the switching elementis delayed with the delay of the control signal, a signal that istransmitted to the inside signal lines is delayed. As a result, sincethe peak level of the potential variation of the common electrode thatis affected by the coupling capacitance with the inside signal lines isdecreased, the potential variation of the common electrode that is setto the reference potential can be suppressed.

(3) The display device according to item (2) further includes: n of thecontrol lines; m of the switching elements which are grouped by n of theswitching elements which is the same number as that of the controllines, and controlled by the respective different control lines in eachgroup; m of the inside signal lines which are electrically connected tothe m switching elements one-on-one; and (m/n) of the outside signallines which are each branched and electrically connected to the nswitching elements in each group, in which when the control signal isinput to one of the n control lines, one of the switching elements ineach group connects one of the outside signal lines and one of theinside signal lines.

(4) The display device according to any one of the items (1) to (3),further includes an insulating film that covers the second portion, inwhich a plurality of contact holes from which the second portion isexposed is formed in the insulating film at intervals in a longitudinaldirection of the second portion.

(5) The display device according to the item (4), further includes aconductive layer which is formed on the insulating film so as to beelectrically connected to the second portion by two or more of thecontact holes, in which the conductive layer is made of a material lowerin electric resistivity than a material of the second portion.

(6) The display device according to the item (4), further includes aradiation layer which is formed on the insulating film so as to come incontact with the second portion by any one of the contact holes, inwhich the radiation layer is made of a material higher in thermalconductivity than a material of the second portion.

(7) In the display device according to any one of the items (1) to (6),the second portion is made of polysilicon.

(8) In the display device according to any one of the items (1) to (7),the second portion extends to draw a straight line.

(9) In the display device according to any one of the items (1) to (7),the second portion has a flexion.

(10) The display device according to anyone of the items (1) to (9)further includes a touch panel that laps over the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of equipment having a display deviceaccording to a first embodiment of the invention;

FIG. 2 is a cross-sectional view illustrating an outline of the displaydevice according to the first embodiment of the invention;

FIG. 3 is a diagram illustrating a substrate of a display panel;

FIG. 4 is a diagram illustrating a circuit for displaying an image;

FIG. 5 is a diagram illustrating the details of an area in which outsidesignal lines are formed;

FIG. 6 is a cross-sectional view taken along a line VI-VI of the areaillustrated in FIG. 5;

FIG. 7 is a cross-sectional view taken along a line VII-VII of the areaillustrated in FIG. 5;

FIG. 8 is a diagram illustrating a modified example 1 of the embodimentillustrated in FIG. 5;

FIG. 9 is a cross-sectional view taken along a line IX-IX of the areaillustrated in FIG. 8;

FIG. 10 is a diagram illustrating a modified example 2 of the embodimentillustrated in FIG. 5;

FIG. 11 is a diagram illustrating a modified example 3 of the embodimentillustrated in FIG. 5;

FIG. 12 is a diagram illustrating a modified example 4 of the embodimentillustrated in FIG. 5;

FIG. 13 is a diagram illustrating a modified example 5 of the embodimentillustrated in FIG. 5;

FIG. 14 is a diagram illustrating a modified example 6 of the embodimentillustrated in FIG. 5;

FIG. 15 is a diagram illustrating a substrate of a display panelprovided in a display device according to a second embodiment of theinvention;

FIG. 16 is a diagram illustrating a circuit for displaying an image;

FIG. 17 is a diagram illustrating control lines;

FIG. 18 is a diagram illustrating a modified example 1 of the secondembodiment; and

FIG. 19 is a diagram illustrating a modified example 2 of the secondembodiment.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the invention will be described withreference to the accompanying drawings.

[First Embodiment]

FIG. 1 is a perspective view of equipment having a display deviceaccording to a first embodiment of the invention. Equipment 1000illustrated in FIG. 1 is an example in which the display device of theinvention is applied to a smart phone, and includes a touch interface.

FIG. 2 is a cross-sectional view illustrating an outline of the displaydevice according to the first embodiment of the invention. The displaydevice has a display panel 10. In this embodiment, the display panel 10is configured by a liquid crystal display panel that includes a pair ofsubstrates 12 and 14 (glass substrates), and a liquid crystal not shownis interposed between those substrates 12 and 14. Polarizing plates 16are attached onto the respective substrates 12 and 14. An integratedcircuit chip 18 that incorporates a driver circuit for driving theliquid crystal is mounted on a peripheral edge portion of one substrate12. A flexible wiring board 20 is also attached onto the peripheral edgeportion thereof. Alternatively, the display panel 10 may be configuredby an organic EL (electro luminescence) panel.

The display device has a touch panel 22 (for example, capacitive typetouch panel 22) . The touch panel 22 and the display panel 10 are bondedtogether by an adhesive layer 24. Since the touch panel 22 laps with thedisplay panel 10 that display an image, a finger input can be conductedon the image. The touch panel 22 is electrically connected with aflexible wiring board 26.

The display device has a cover substrate 28. The cover substrate 28 ismade of a light transmissive material (for example, glass) . A lightshield film 30 is formed on the cover substrate 28 so as to surround anarea where the image is displayed. A surface of the cover substrate 28on which the light shield film 30 is formed is attached to the touchpanel 22 through an adhesive layer 31.

FIG. 3 is a diagram illustrating the substrate 12 of the display panel10. The substrate 12 has an image display area 32.

In the image display area 32, an image is configured by a plurality ofpixels. The plurality of pixels is driven by a driver circuitincorporated into the integrated circuit chip 18 also illustrated inFIG. 2 to change a level of brightness. Because the driving is conductedby a scanning system, the substrate 12 is formed with scanning circuits34. For example, the respective scanning circuits 34 are formed adjacentto two opposite sides of the rectangular image display area 32, and theintegrated circuit chip 18 is mounted adjacent to another side of theimage display area 32.

FIG. 4 is a diagram illustrating a circuit for displaying the image.Pixel electrodes 36 are formed in the image display area 32. Since thepixels are formed by the plurality of pixel electrodes 36, an areasurrounding the plurality of pixel electrodes 36 configures the imagedisplay area 32. A common electrode 38 is formed in the image displayarea 32. A potential of the common electrode 38 is set to a referencepotential (for example, GND), and a voltage corresponding to thebrightness of each pixel is applied to each of the pixel electrodes 36.An image is displayed under the control (for example, driving of theliquid crystal) of the light using the electric field developed betweeneach of the pixel electrodes 36 and the common electrode 38.

The common electrode 38 is electrically connected to a common line 40extending inside and outside the image display area 32. The pixelelectrodes 36 are electrically connected to signal lines 42. In detail,a switching element 44 (for example, thin film transistor) is connectedbetween each of the pixel electrodes 36 and each of the signal lines 42to conduct electric continuity and discontinuity between the pixelelectrode 36 and the signal line 42. The switching element 44 isconnected to each of scanning lines 46 taken out of the scanning circuit34, and driven (turned on/off) according to a scanning signal input tothe scanning line 46.

The signal line 42 includes an inside signal line 41 present inside theimage display area 32, and an outside signal line 43 present outside theimage display area 32. The inside signal line 41 is electricallyconnected to the pixel electrode 36. The inside signal line 41 is madeof a material low in electric resistivity such as metal. Because theinside signal line 41 extends in proximity to the common electrode 38, acoupling capacitance C is formed between the inside signal line 41 andthe common electrode 38. The potential of the common electrode 38 to beset to the reference potential is changed by the coupling capacitance C,but this embodiment has the following features for the purpose ofsuppressing the variation thereof.

FIG. 5 is a diagram illustrating the details of an area in which outsidesignal lines are formed. FIG. 6 is a cross-sectional view taken along aline VI-VI of the area illustrated in FIG. 5. FIG. 7 is across-sectional view taken along a line VII-VII of the area illustratedin FIG. 5.

The outside signal line 43 includes a first portion 48 and a secondportion 50. The first portion 48 is made of a material low in theelectric resistivity such as metal, and may be made of the same materialas that of the inside signal line 41. The second portion 50 is higher inelectric resistance than the first portion 48, and made of, for example,a material (for example, semiconductor material) high in electricresistivity. Also, the second portion 50 is made of a material higher inelectric resistivity than the inside signal line 41 illustrated in FIG.4. In an example of FIG. 5, the second portion 50 is situated on a sidecloser to the inside signal line 41, and the first portion 48 issituated on a side farther from the inside signal line 41, and viceversa. Also, the second portion 50 may be disposed between a pair of thefirst portions 48, or the first portion 48 may be disposed between apair of the second portions 50. In this embodiment, as illustrated inFIG. 3, the first portion 48 is electrically connected to a drivercircuit incorporated into the integrated circuit chip 18.

In an area where the outside signal lines 43 (second portions 50) areformed, as illustrated in FIGS. 6 and 7, a plurality of films arelaminated on the substrate 12. The plurality of films includes asemiconductor film 52 (for example, polysilicon film). The semiconductorfilm 52 configures a part of the thin film transistor (switching element44 illustrated in FIG. 4). The semiconductor film 52 is covered with agate insulating film 54, and the thin film transistor has a gateelectrode (not shown) on the gate insulating film 54. An interlayerinsulating film 56 is formed on the gate insulating film 54. In thisembodiment, the second portion 50 (FIG. 5) is formed of thesemiconductor film 52. More specifically, the second portion 50 is madeof polysilicon.

According to this embodiment, the second portion 50 is higher inelectric resistance than the first portion 48. That is, the electricresistance of apart of the outside signal line 43 is higher.

Accordingly, a signal that is transmitted to the inside signal line 41is delayed by the height of electric resistance of the second portion 50when passing through the outside signal line 43. The signal delaydecreases the peak level of the potential variation of the commonelectrode 38 which is affected by the coupling capacitance C with theinside signal line 41. As a result, the potential variation of thecommon electrode 38 set to the reference potential can be suppressed.

The second portion 50 (semiconductor film 52) is covered with aninsulating film (the gate insulating film 54 and the interlayerinsulating film 56). A plurality of contact holes 58 that exposes thesecond portion 50 (the semiconductor film 52) is formed in theinsulating film (the gate insulating film 54 and the interlayerinsulating film 56) at intervals in a longitudinal direction of thesecond portion 50 (refer to FIG. 5). An electric connection with thesecond portion 50 is enabled through the contact holes 58. If twoportions of the second portion 50 distant from each other areelectrically connected to each other through the two contact holes 58distant from each other in the longitudinal direction of the secondportion 50, an electric resistance between the two distant portions canbe decreased. In the example of FIG. 5, the two contact holes 58 arealigned in a width direction of the second portion 50. This is becausethe electric connection with the second portion 50 is ensured.

In this embodiment, the two distant portions of the second portion 50are not electrically connected to each other. However, a conductivelayer 60 is formed over the inside of the contact holes 58 from abovethe insulating film (interlayer insulating film 56) so as to beelectrically connected to the second portion 50 in the respectivecontact holes 58. That is, exposed portions of the second portion 50from the insulating film are electrically connected to each other by theconductive layer 60. The conductive layer 60 is made of a material (forexample, metal) lower in the electric resistivity than the material ofthe second portion 50. The electric connection of the two distantportions of the second portion 50 is enabled by merely changing a shapeof the conductive layer 60. The detail will be described in thefollowing modified example. An inorganic passivation film 62, an organicpassivation film 64, and another inorganic passivation film 66 arelaminated on the conductive layer 60 in the stated order.

[Modified Example]

FIG. 8 is a diagram illustrating a modified example 1 of the embodimentillustrated in FIG. 5. FIG. 9 is a cross-sectional view taken along aline IX-IX of the area illustrated in FIG. 8. In this example, aconductive layer 160 is formed on the insulating film. The conductivelayer 160 is so formed as to pass through two or more contact holes 158distant from each other in a longitudinal direction of a second portion150. The conductive layer 160 is electrically connected to the secondportion 150 in the contact holes 158. That is, the portions of thesecond portion 150 distant in the longitudinal direction areelectrically connected to each other by the conductive layer 160 in thetwo or more contact holes 158 distant from each other in thelongitudinal direction of the second portion 150. Since the conductivelayer 160 is lower in the electric resistance than the second portion150, the electric resistance between the two distant portions of thesecond portion 150 can be decreased by the conductive layer 160. Thedecrease in the electric resistance makes it possible to adjust thedegree of the signal delay caused by the height of electric resistanceof the second portion 150.

The conductive layer 160 can electrically connect the portions of thesecond portion 150 present at an arbitrary distance, and can beelectrically connected with the second portion 150 by an arbitrarynumber of contact holes 158. For example, FIG. 8 illustrates aconductive layer 160 a which is electrically connected with the secondportion 150 in the two contact holes 158 present at a first distance d₁in the longitudinal direction of the second portion 150, a conductivelayer 160 b which is electrically connected with the second portion 150in a pair of contact holes 158 present at a second distance d₂ in thelongitudinal direction of another second portion 150, and one contacthole 158 located between those contact holes, and further a conductivelayer 160 c which is electrically connected with the second portion 150in a pair of contact holes 158 present at a third distance d₃ in thelongitudinal direction of another second portion 150, and a plurality(two) of contact holes 158 located between those contact holes.

FIG. 10 is a diagram illustrating a modified example 2 of the embodimentillustrated in FIG. 5. In this example, a radiation layer 268 is formedon the insulating film so as to contact with a second portion 250 in anycontact hole 258. The radiation layer 268 is higher in radiationproperty with a larger size. The radiation layer 268 is made of amaterial higher in the thermal conductivity than the material of thesecond portion 250. The radiation layer 268 may be formed of aconductive layer.

FIG. 11 is a diagram illustrating a modified example 3 of the embodimentillustrated in FIG. 5. In the example illustrated in FIG. 5, the secondportion 50 is lengthened with the provision of the flexion to increasethe overall electric resistance. On the other hand, in the exampleillustrated in FIG. 11, since a second portion 350 straight extends soas to draw a straight line, the electric resistance becomes relativelylow.

FIG. 12 is a diagram illustrating a modified example 4 of the embodimentillustrated in FIG. 5. In the example illustrated in

FIG. 5, the second portion 50 is so bent as to alternately formconvexes. On the other hand, in the example illustrated in FIG. 12, asecond portion 450 is so bent as to form the convexes in the samedirection.

FIG. 13 is a diagram illustrating a modified example 5 of the embodimentillustrated in FIG. 5. The second portion 50 illustrated in FIG. 5 is sobent as to form one convex between a pair of contact holes 58 distant inthe longitudinal direction of the second portion 50. On the contrary, asecond portion 550 illustrated in FIG. 13 is so bent as to form aplurality (for example, two) of convexes between a pair of contact holes558 distant in the longitudinal direction of the second portion 550. Theplurality of convexes may be protruded in opposite directions to eachother as illustrated in FIG. 13, or may be protruded in the samedirection.

FIG. 14 is a diagram illustrating a modified example 6 of the embodimentillustrated in FIG. 5. In this example, a second portion 650 is bentinto a crank shape between a pair of contact holes 658 distant in thelongitudinal direction of the second portion 650.

[Second Embodiment]

FIG. 15 is a diagram illustrating a substrate of a display panelprovided in a display device according to a second embodiment of theinvention. FIG. 16 is a diagram illustrating a circuit for displaying animage.

The display device includes a substrate 712 having an image display area732. Inside signal lines 741 are formed inside the image display area732. Outside signal lines 743 are formed outside the image display area732. A common line 740 is so formed as to pass inside and outside theimage display area 732.

The display device according to this embodiment includes the pixelelectrodes 36 and the common electrode 38 described in the firstembodiment illustrated in FIG. 4, and displays an image under thecontrol of a light using an electric field developed between the pixelelectrodes 36 and the common electrode 38. The details are identicalwith those described in the first embodiment. This embodiment is alsoidentical with the first embodiment in that the coupling capacitance Cis formed between the inside signal line 41 and the common electrode 38.

As illustrated in FIG. 16, the display device according to thisembodiment is different from the first embodiment in that an RGBselector circuit 772 is provided. The number of outside signal lines 743can be reduced by the RGB selector circuit 772.

In more detail, the RGB selector circuit 772 has m (m=6 in FIG. 16)switching elements 744. The respective switching elements 744 switchelectric continuity and discontinuity between the inside signal lines741 and the outside signal lines 743. The respective switching elements744 receive control signals from control lines 770. When the controlsignals are input to the respective control lines 770, the respectiveswitching elements 744 connect the outside signal lines 743 to theinside signal lines 741.

The number of control lines 770 is n (n=3 in FIG. 16). The m switchingelements 744 are grouped by n switching elements 744 which is the samenumber as that of the control lines 770. The n switching elements 744 ineach group are controlled by the respective different control lines 770.The m switching elements 744 are electrically connected to the m insidesignal lines 741 one-on-one. Each of the (m/n) outside signal lines 743is branched into n lines so as to be electrically connected to the nswitching elements in each group. When the control signal is input toone of the n control lines 770, one switching element 744 in each groupconnects one outside signal line 743 and one inside signal line 741.

A plurality of pixels aligned along one scanning line (not shown) hasred pixels R₁, R₂, . . . , green pixels G₁, G₂, . . . , and blue pixelsB₁, B₂, . . . The control lines 770 are connected to the RGB selectorcircuit 772 so as to select any color. For that reason, the number ofpixel colors (three colors of RGB) is identical with the number ofcontrol lines 770. When any color is selected by the control lines 770,a signal is input to the pixels of the selected color from signal lines742 (outside signal lines 743).

For example, when the red pixels R₁ and R₂ are selected, the controlsignal is input to a control line 770 _(R). Then, the switching element744 _(R1) and the switching elements 744 _(R2) turn on to connect theoutside signal line 743 a and the inside signal line 741 _(R1), andconnect the outside signal line 743 b and the inside signal line 741_(R2). In this situation, the signals corresponding to the red pixels R₁and R₂ are input to the outside signal line 743 a and the outside signalline 743 b, respectively, to display the red pixels R₁ and R₂ accordingto the signal.

When the green pixels G₁ and G₂ are selected, the control signal isinput to a control line 770 _(G). Then, the switching element 744 _(G1)and the switching elements 744 _(G2) turn on to connect the outsidesignal line 743 a and the inside signal line 741 _(G2), and connect theoutside signal line 743 b and the inside signal line 741 _(G1). In thissituation, the signals corresponding to the green pixels G₁ and G₂ areinput to the outside signal line 743 a and the outside signal line 743b, respectively, to display the green pixels G₁ and G₂ according to thesignal.

When the blue pixels B₁ and B₂ are selected, the control signal is inputto a control line 770 _(B). Then, the switching element 744 _(B1) andthe switching elements 744 _(B2) turn on to connect the outside signalline 743 a and the inside signal line 741 _(B1), and connect the outsidesignal line 743 b and the inside signal line 741 _(B2). In thissituation, the signals corresponding to the blue pixels B₁ and B₂ areinput to the outside signal line 743 a and the outside signal line 743b, respectively, to display the blue pixels B₁ and B₂ according to thesignal.

FIG. 17 is a diagram illustrating the control lines 770. Each of thecontrol lines 770 includes a first portion 748 and a second portion 750.The first portion 748 is made of a material low in electric resistivitysuch as metal, and may be made of the same material as that of theinside signal lines 741. The second portion 750 is higher in electricresistance than the first portion 748. In this example, the secondportion 750 is formed thinner (narrower in width) than the first portion748 so as to increase the electric resistance. Accordingly, the secondportion 750 is made of the same material (for example, metal) as that ofthe first portion 748. This is also applicable to the first embodiment.Conversely, as described in the first embodiment, the second portion 750may be made of a material (for example, semiconductor material such aspolysilicon) higher in electric resistivity than that of the firstportion 748 or the inside signal lines 741.

According to this embodiment, the control signal that is input to theswitching elements 744 is delayed by the height of electric resistanceof the second portion 750 when passing through the control line 770.Since the delay of the control signal delays the operation of theswitching elements 744, the signal which is transmitted to the insidesignal lines 741 is delayed. This decreases the peak level of thepotential variation of the common electrode (not shown) which isaffected by the coupling capacitance with the inside signal lines 741.As a result, the potential variation of the common electrode (not shown)set to the reference potential can be suppressed.

[Modified Example]

FIG. 18 is a diagram illustrating a modified example 1 of the secondembodiment. In this example, a conductive layer 860 is so formed as tobe electrically connected to a second portion 850. In more detail,although the second portion 850 is made of metal, the second portion 850is high in the electric resistance because of a thin configuration. Theportions of the second portion 850 distant in the longitudinal directionare electrically connected by the conductive layer 860 in two or morecontact holes 858 distant in the longitudinal direction of the secondportion 850. Since the conductive layer 860 is wider in width than thesecond portion 850, the electric resistance becomes low. For thatreason, the electric resistance between the two distant portions of thesecond portion 850 can be decreased by the conductive layer 860. Thedecrease in the electric resistance makes it possible to adjust thedegree of the signal delay caused by the height of electric resistanceof the second portion 850.

FIG. 19 is a diagram illustrating a modified example 2 of the secondembodiment. Similarly, in this example, a conductive layer 960 canelectrically connect portions of a second portion 950 present at anarbitrary distance, and can be electrically connected with the secondportion 950 by contact holes 958 of an arbitrary number. For example,FIG. 19 illustrates a conductive layer 960 a which is electricallyconnected with the second portion 950 in the two contact holes 958present at a first distance d₁₁ in the longitudinal direction of thesecond portion 950, a conductive layer 960 b which is electricallyconnected with the second portion 950 in a pair of contact holes 958present at a second distance d₂₂ in the longitudinal direction ofanother second portion 950, and one contact hole 958 located betweenthose contact holes, and further a conductive layer 960 c which iselectrically connected with the second portion 950 in a pair of contactholes 958 present at a third distance d₃₃ in the longitudinal directionof another second portion 950, and a plurality (two) of contact holes958 located between those contact holes.

While there have been described what are at present considered to becertain embodiments of the invention, it will be understood that variousmodifications may be made thereto, and it is intended that the appendedclaims cover all such modifications as fall within the true spirit andscope of the invention.

What is claimed is:
 1. A display device comprising: a substrate havingan image display area; pixel electrodes formed in the image display areaof the substrate; a common electrode formed in the image display area ofthe substrate; inside signal lines formed inside the image display areaof the substrate, and electrically connected to the pixel electrodes;outside signal lines formed outside the image display area of thesubstrate, and electrically connected to the inside signal lines; acommon line formed inside and outside the image display area of thesubstrate, and electrically connected to the common electrode, whereinan image is displayed under a control of a light using an electric fielddeveloped between the pixel electrodes and the common electrode, whereina coupling capacitance is formed between the inside signal lines and thecommon electrode, wherein the outside signal lines includes a firstportion, and a second portion that is higher in electric resistance thanthe first portion, wherein the second portion has a bend, and wherein alayer of the first portion is different from a layer of the secondportion.
 2. The display device according to claim 1, further comprising:an insulating film that covers the second portion, wherein a pluralityof contact holes from which the second portion is exposed are formed inthe insulating film at intervals in a longitudinal direction of thesecond portion.
 3. The display device according to claim 2, furthercomprising: a conductive layer formed on the insulating film so as to beelectrically connected to the second portion by two or more of thecontact holes, wherein the conductive layer is made of a material lowerin electric resistivity than a material of the second portion.
 4. Thedisplay device according to claim 1, wherein the second portion is madeof polysilicon.
 5. The display device according to claim 1, wherein thesecond portion extends to draw a straight line.
 6. A display devicecomprising: a substrate having an image display area; pixel electrodesformed in the image display area of the substrate; a common electrodeformed in the image display area of the substrate; inside signal linesformed inside the image display area of the substrate, and electricallyconnected to the pixel electrodes; outside signal lines formed outsidethe image display area of the substrate; switching elements each ofwhich switches electric continuity and discontinuity between the insidesignal lines and the output signal lines; control lines that input acontrol signal to the switching elements; and a common line formedinside and outside the image display area of the substrate, andelectrically connected to the common electrode, wherein an image isdisplayed under a control of a light using an electric field developedbetween the pixel electrodes and the common electrode, wherein acoupling capacitance is formed between the inside signal lines and thecommon electrode, wherein the control lines each include a firstportion, and a second portion higher in electric resistance than thefirst portion, and wherein the first portion has a width wider than thatof the second portion, and wherein a layer of the first portion isdifferent from a layer of the second portion.
 7. The display deviceaccording to claim 6, further comprising an insulating film that coversthe second portion, wherein a plurality of contact holes from which thesecond portion is exposed is formed in the insulating film at intervalsin a longitudinal direction of the second portion.
 8. The display deviceaccording to claim 7, further comprising a conductive layer formed onthe insulating film so as to be electrically connected to the secondportion by two or more of the contact holes, wherein the conductivelayer is made of a material lower in electric resistivity than amaterial of the second portion.
 9. The display device according to claim6, wherein the second portion is made of polysilicon.
 10. The displaydevice according to claim 6, wherein the second portion extends to drawa straight line.